The Benefits of CSS. Less work: Change look of the whole site with one edit

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1 11 INTRODUCING CSS

2 OVERVIEW The benefits of CSS Inheritance Understanding document structure Writing style rules Attaching styles to the HTML document The cascade The box model CSS units of measurement

3 The Benefits of CSS Precise type and layout control Less work: Change look of the whole site with one edit Accessibility: Markup stays semantic Flexibility: The same HTML markup can be made to appear in dramatically different ways

4 Style Separate from Structure These pages have the exact same HTML source but different style sheets: (csszengarden.com)

5 How Style Sheets Work 1. Start with a marked up document (like HTML, but could be another XML markup language). 2. Write styles for how you want elements to look using CSS syntax. 3. Attach the styles to the document (there are a number of ways). 4. The browser uses your instructions when rendering the elements.

6 Style Rules Each rule selects an element and declares how it should display. h1 { color: green; } This rule selects all h1 elements and declares that they should be green. strong { color: red; font-style: italic; } This rule selects all strong inline elements and declares that they should be red and in an italic font.

7 Style Rule Structure A style rule is made up of a selector a declaration. The declaration is one or more property / value pairs.

8 Selectors There are many types of selectors. Here are just two examples: p {property: value;} Element type selector: Selects all elements of this type (p) in the document. #intro {property: value} ID selector (indicated by the # symbol) selects by ID value. In the example, an element with an id of intro would be selected.

9 Declarations The declaration is made up of a property/value pair contained in curly brackets { }: selector { property: value; } Example h2 { color: red; font-size: 2em; margin-left: 30px; opacity:.5; }

10 Declarations (cont d) End each declaration with a semicolon to keep it separate from the next declaration. White space is ignored, so you can stack declarations to make them easier to read. Properties are defined in the CSS specifications. Values are dependent on the type of property: Measurements Keywords Color values More

11 CSS Comments /* comment goes here */ Content between /* and */ will be ignored by the browser. Useful for leaving notes or section labels in the style sheet. Can be used within rules to temporarily hide style declarations in the design process.

12 Adding Styles to the Document There are three ways to attach a style sheet to a document: External style sheets A separate, text-only.css file associated with the document with the link element rule Embedded style sheets Styles are listed in the head of the HTML document in the style element. Inline styles Properties and values are added to an individual element with the style attribute.

13 External Style Sheets The style rules are saved in a separate text-only.css file and attached via link Via link element in HTML: <head> <title>titles are require</title> <link rel="stylesheet" href="/path/example.css"> </head> rule in a style sheet: <head> <title>titles are required</title> url("/path/example.css"); p {font-face: Verdana;} </style> </head>

14 Embedded Style Sheets Embedded style sheets are placed in the head of the document via the style element: <head> <title>titles are required</title> <style> /* style rules go here */ </style> </head>

15 Inline Styles Apply a style declaration to a single element with the style attribute: <p style="font-size: large;">paragraph text...</p> To add multiple properties, separate them with semicolons: <h3 style="color: red; margin-top: 30px;">Intro</h3>

16 Document Structure Documents have an implicit structure. We give certain relationships names, as if they re a family: All the elements contained in a given element are its descendents. An element that is directly contained within another element is the child of that element. The containing element is the parent of the contained element. Two elements with the same parent are siblings.

17 Inheritance Many properties applied to elements are passed down to the elements they contain. This is called inheritance. For example, applying a sans-serif font to a p element causes the em element it contains to be sans-serif as well:

18 Inheritance (cont d) Some properties inherit; others do not. Properties related to text usually inherit; properties related to layout generally don t. Styles explicitly applied to specific elements override inherited styles. You ll learn to use inheritance strategically to keep your style rules simple.

19 The Cascade The cascade refers to the system for resolving conflicts when several styles apply to the same element. Style information is passed down (it cascades down) until overwritten by a style rule with more weight. Weight is considered based on: Priority of style rule source Specificity of the selector Rule order

20 The Cascade: Priority Style rules from sources higher in this list override rules from sources listed below them. Any style marked as!important by the user (to accommodate potential accessibility settings) Any style marked!important by the author (of the web page) Author styles (style sheets created in web site production) User styles (added by the reader) User agent styles (browser defaults)

21 The Cascade: Specificity When two rules in a single style sheet conflict, the type of selector is used to determine which rule has more weight. For example, ID selectors are more specific than general element selectors. NOTE: Specificity will be discussed once we have covered more selector types.

22 The Cascade: Rule Order When two rules have equal weight, rule order is used. Whichever rule appears last wins. <style> p {color: red;} p {color: blue;} p {color: green;} </style> In this example, paragraphs would be green. Styles may come in from external style sheets, embedded style rules, and inline styles. The style rule that gets parsed last (the one closest to the content) will apply.

23 The Box Model Browsers see every element on the page as being contained in a little rectangular box. Block elements and inline elements participate in the box model. In this example, a blue border is added to all elements.

24 The Box Model (cont d) The box model is the foundation of CSS page layout. Apply properties such as borders, margins, padding, and backgrounds to element boxes. Position, move, grow, and shrink boxes to create fixed or flexible page layouts.

25 CSS Units of Measurement CSS provides a variety ways to specify measurements: Absolute units Have predefined meanings or real-world equivalents Relative units Based on the size of something else, such as the default text size or the size of the parent element Percentages Calculated relative to another value, such as the size of the parent element

26 Absolute Units With the exception of pixels, absolute units are not appropriate for web design: px in mm cm q pt pc pixel inches millimeters centimeters 1/4 millimeter points (1/72 inch) pica (1 pica = 12 points = 1/6 inch)

27 Relative Units Relative units are based on the size of something else: em a unit equal to the current font size ex x-height, equal to the height of a lowercase x rem root em, equal to the font size of the html element ch zero width, equal to the width of a zero (0) vw viewport width unit (equal to 1/100 of viewport width) vh viewport height unit (1/100 of viewport height) vmin viewport minimum unit (value of vh or vw, whichever is smaller) vmax viewport maximum unit (value of vh or vw, whichever is larger)

28 RELATIVE UNITS The rem Unit The rem (root em) unit is based on the font size of the html element, whatever that happens to be. Default in modern browsers: Root font size is 16 pixels, so a rem = a 16-pixel unit. If the root font size of the document changes, so does the size of a rem (and that s good for keeping elements proportional).

29 RELATIVE UNITS The em Unit The em unit is traditionally based on the width of a capital letter M in the font. When the font size is 16 pixels,1em = 16 pixels, 2em = 32 pixels, and so on. NOTE: Because they re based on the font size of the current element, the size of an em may not be consistent across a page.

30 RELATIVE UNITS Viewport Percentage Lengths (vw/vh) Viewport width (vw) and viewport height (vh) units are relative to the size of the viewport (browser window): vh = 1/100th width of viewport vh = 1/100th height of viewport They re useful for making an element fill the viewport or a specified percentage of it. This image will be 50% the width and height of the viewport: img { width: 50vw; height: 50vh; }

31 Browser Developer Tools Major browsers have built-in tools that aid development: HTML, CSS, and JavaScript inspectors Network speed reports Animation tools Other helpful features

32 Browser Developer Tools (cont d) Chrome DevTools (View > Developer > Developer Tools) Firefox, Safari, Opera, and Microsoft Edge also have developer tools.

2. Write style rules for how you d like certain elements to look.

2. Write style rules for how you d like certain elements to look. CSS for presentation Cascading Style Sheet Orientation CSS Cascading Style Sheet is a language that allows the user to change the appearance or presentation of elements on the page: the size, style, and